Highlights
- BCR::ABL1 tyrosine kinase inhibitors (TKIs) induce nuclease-resistant ribosome collisions in chronic myeloid leukemia (CML) cells.
- The kinase ZAK serves as a molecular sensor of these collisions, initiating the ribotoxic stress response (RSR) and p38-mediated apoptosis.
- ZAK expression increases as CML progresses from chronic phase to blast phase, where it sustains proliferation through AKT signaling but sensitizes cells to TKI-induced death.
- Targeting the translational and metabolic machinery—including the mTOR-EEF2K axis and mitochondrial OXPHOS—presents new opportunities to overcome TKI resistance.
Background
Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm driven by the constitutively active tyrosine kinase BCR::ABL1. The advent of tyrosine kinase inhibitors (TKIs) such as imatinib, dasatinib, and ponatinib has transformed CML into a manageable chronic condition for many. However, a subset of patients progresses to the aggressive blast phase (CML-BP) or develops resistance, often through BCR::ABL1-independent mechanisms including metabolic reprogramming, epigenetic alterations, and aberrant translational regulation. Recent research has shifted focus from purely genomic drivers to the cellular ‘proteostasis’ and stress response networks. Specifically, the concept of ribosome collisions—where multiple ribosomes stall and ‘crash’ into one another during translation elongation—has emerged as a vital sensor of cellular health. The recent discovery that TKIs actively leverage this ribotoxic stress response (RSR) to eliminate leukemic cells provides a paradigm-shifting view of how targeted therapies function at a biophysical level.
Key Content
1. The Mechanistic Nexus: Ribosome Collisions and ZAK Activation
The primary mechanism by which BCR::ABL1 inhibitors exert their cytotoxic effect was traditionally thought to be the simple withdrawal of survival signals. However, Park et al. (2026) have demonstrated that BCR::ABL1 inhibition fundamentally disrupts translation elongation. Mechanistically, TKI treatment suppresses the mTOR pathway, which normally inhibits eukaryotic translation elongation factor 2 kinase (EEF2K). When BCR::ABL1 is inhibited, EEF2K becomes active and phosphorylates EEF2, significantly slowing the movement of ribosomes along mRNA. This ‘traffic jam’ results in nuclease-resistant collided ribosomes (disomes and trisomes).
These collisions are sensed by the MAP3K member ZAK (also known as MAP3K20). ZAK specifically binds to the unique structure formed by collided ribosomes, undergoing autophosphorylation and subsequently activating the p38 MAPK pathway. This activation is the ‘point of no return’ that triggers apoptosis in CML cells. Paradoxically, while ZAK is required for the cell death induced by TKIs, it also plays a pro-proliferative role in the absence of drug stress by promoting AKT activity, particularly in advanced stages of the disease.
2. Disease Progression and ZAK Dysregulation
Clinical analyses of patient samples indicate that ZAK expression is not uniform across CML stages. Progression from the chronic phase (CML-CP) to the blast phase (CML-BP) is associated with a marked upregulation of ZAK. This elevated expression likely supports the high proliferative demand of blast cells via AKT signaling. However, this also creates a ‘therapeutic vulnerability’; high-ZAK-expressing cells are more susceptible to RSR-mediated apoptosis when treated with TKIs, provided the elongation block is sufficiently strong. This dual role of ZAK explains why its loss can lead to TKI resistance, as the cells lose their ability to sense translational stress and initiate the apoptotic program.
3. Alternative Pathways and Translation-Related Resistance
Other studies complement this translational landscape. For instance, the deubiquitinating enzyme USP8 has been found to stabilize EIF2S1 (eIF2α), a key factor in translation initiation. High levels of USP8 prevent EIF2S1 degradation, sustaining high rates of translation even under stress, thereby contributing to TKI resistance (PMID: 41147744). Similarly, METTL14-driven m6A modification of Bcl-x mRNA alters splicing patterns to favor the anti-apoptotic Bcl-xL isoform, further shielding cells from the death signals initiated by ribosome collisions (PMID: 40760738). These findings suggest that CML cells employ a multi-layered defense to prevent translation-induced stress from reaching the apoptotic threshold.
4. Metabolic Reprogramming as a Shield Against RSR
Metabolic plasticity is intrinsically linked to translational stress. CML-BP cells often exhibit enhanced glycolysis and mitochondrial alterations. Studies have shown that p38 MAPK (the downstream effector of ZAK) can sometimes be diverted to mediate metabolic rewiring. In imatinib-resistant CML-BC cells, p38 MAPK-mediated suppression of the Nrf2-MPC2 axis abrogates mitochondrial function to prevent ROS-mediated death while shifting the energy burden to glycolysis (PMID: 41423144). Furthermore, bone marrow stromal cells have been shown to ‘rescue’ leukemic cells by transferring TCA-related proteins via vesicles, thereby maintaining metabolic stability and preventing the energy collapse required for efficient TKI-induced apoptosis (PMID: 41331927).
5. Novel Therapeutic Strategies to Sensitize CML Cells
Given the central role of ribosome collisions, pharmacological modulation of translation flux is a promising adjunctive strategy. Potentiating the elongation block or inhibiting the ‘escape’ pathways (like autophagy or specific deubiquitinases) can resensitize resistant cells:
- Synergistic Combinations: Combining TKIs with inhibitors of MSI2 (an RNA-binding protein) has shown synergistic effects by disrupting Wnt/β-catenin signaling and inducing p53-mediated stress (PMID: 41353321).
- Natural Products: Caffeic acid phenethyl ester (CAPE) and Cannabidiol (CBD) have been investigated for their ability to inhibit mitochondrial complex I and modulate exosomal miRNA networks, respectively, creating a cellular environment where TKIs can more easily trigger RSR (PMID: 41486183, 41657764).
- Direct Targeting of RSR: Experimental modulation of translation flux has already been shown to fine-tune TKI efficacy in primary patient cells, suggesting that ‘elongation-slowing’ agents could be a future class of TKI-potentiators.
Expert Commentary
The identification of the ZAK-dependent RSR pathway in CML represents a major leap in our understanding of TKI pharmacology. Historically, drug development focused on increasing the affinity of TKIs for the BCR::ABL1 ATP-binding pocket. While this led to potent second- and third-generation inhibitors like ponatinib and asciminib, it did not address the fundamental ways in which cells ‘ignore’ the lack of BCR::ABL1 signaling. The RSR model suggests that the efficacy of a TKI is not just determined by kinase inhibition but by the resulting biophysical stress on the ribosome.
Clinical implications are significant. ZAK expression levels could potentially serve as a biomarker to predict TKI response or the likelihood of progression. However, a controversy remains: since ZAK promotes AKT-driven proliferation in the blast phase, would inhibiting ZAK be beneficial or detrimental? The evidence suggests that while ZAK inhibition might slow growth, it would also provide a ‘survival shield’ against TKIs. Therefore, the strategy should likely be to hyper-activate the RSR pathway during TKI therapy rather than inhibiting it. Additionally, the cardiotoxicity associated with potent TKIs like ponatinib, recently shown to be ameliorated by BMP-7 in murine models (PMID: 41471266), reminds us that systemic stress responses must be managed carefully to maintain a therapeutic window.
Conclusion
The discovery that BCR::ABL1 TKIs induce ribosome collisions to activate ZAK-dependent apoptosis defines a new mechanistically driven framework for CML therapy. As the disease progresses, the cell’s reliance on ZAK for proliferation creates a unique vulnerability that can be exploited by targeted inhibitors. Future research should prioritize the development of translation-modulating agents that can ensure ribosome collisions reach the critical threshold required for apoptosis, especially in leukemia stem cells and blast-phase populations that currently evade standard therapy. Integrating metabolic and translational biomarkers into clinical trials will be essential for the next generation of precision medicine in CML.
References
- Park J, et al. BCR::ABL1 tyrosine kinase inhibitors induce ribosome collisions to activate ZAK-dependent ribotoxic stress and apoptosis in chronic myeloid leukemia. Leukemia. 2026. PMID: 41912913.
- Zhao X, et al. The deubiquitinating enzyme USP8 promotes tyrosine kinase inhibitors resistance in chronic myeloid leukemia by stabilizing EIF2S1 protein. FEBS J. 2026. PMID: 41147744.
- Kumar A, et al. p38 MAPK-mediated suppression of Nrf2-MPC2 axis drives metabolic reprogramming which confers imatinib resistance in blast crisis phase of chronic myeloid leukemia. Exp Cell Res. 2026. PMID: 41423144.
- Saha S, et al. Targeting Musashi-2 to counteract senescence and resistance in chronic myeloid leukemia. BMC Cancer. 2025. PMID: 41353321.
- Stroma-driven horizontal transfer of TCA-related proteins mediates metabolic plasticity and imatinib resistance in chronic myeloid leukemia. Cell Commun Signal. 2025. PMID: 41331927.